Networks are multi-layered in nature, such as abstracted by the Open Systems Interconnection model of Layers 1 through 7 (L1-L7). For descriptions herein, an additional Layer 0 is described as the physical photonic/Dense Wavelength Division Multiplexing (DWDM) network, whereas Layer 1 is used for Optical Transport Network (OTN) or other Time Division Multiplexing (TDM) protocols. For example, with optical networks, a circuit switching layer (L1) (e.g., OTN, Synchronous Optical Network (SONET), etc.) relies on underlying DWDM (L0) with various Reconfigurable Optical Add/Drop Multiplexers (ROADMs). Above the circuit switching layer, packet connectivity such as Ethernet, Internet Protocol (IP), etc. can add to the network hierarchy, e.g., L2+. In this hierarchy, a server layer is typically responsible for physical connectivity, and a client layer is responsible for fast reroutes, flow control, Quality of Service (QoS), etc. For example, DWDM can be the server layer whereas OTN is the client layer.
One problem with this model is that multiple links in the client layer could be physically co-routed in the underlying server layer. Thus, a single failure in the server layer could lead to multiple failures in the client layer. The operational costs associated with protection bandwidth provisioning in a multi-layer architecture impacts network economics. Existing L1 network overlay design is a manual process whereby resiliency is achieved by trying to lay down L1 links over L0 paths to maximize resiliency. This process becomes complicated as the L0/1 network complexity increases. The result can be an ad-hoc network design that has non-optimal resiliency capability given the cost of the network—that is to say for the same amount of equipment a higher level of resiliency is achievable. Existing L0 network control plane functions resolve failures without any consideration for the overlay network. The result of this is a steady erosion of the resiliency that was originally designed into the network through non-optimal restoration path selection, possibly leading to partitioning of the client layer given failures in the server layer.
It would be advantageous to optimize a client layer given a server layer (or vice versa, i.e., optimize the server layer given the client layer).